U.    S.    D.    A. 


Exhibit  of  the  Office  of 
Public  RoadB% 
AlaflkcuYukon^Pacific 

Expos it ion, 190$ 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

OFFICE    OF    PUBLIC    ROAD8, 

LOG;LN  WALLER  PAGE,  DIRBCTOK. 


EXHIBIT  OF  THE 
OFFICE  OF  PUBLIC  ROADS 

AI^\SKA-YUKO:s -PACIFIC  EXPOSITION. 


WASHINGTOl 

GOVERNMENT     i    .  FICE 

19" 


OFFICE  OF  PUBLIC  ROADS. 


LOGAN  WALLER  PAGE,  Director. 

ALLEBTON  S.  CUSHMAN,  Assistant  Director  and  Chemist. 

W.  GAEL  WYATT,  Chief  Clerk. 

VEENON  M.  PEISCE,  Chief  Engineer. 

J.  E.  PENNYBACKER,  Jr.,  Chief  of  Road  Management. 

MAUBICE  O.  ELDBIDGE,  Assistant  Chief  of  Road  Management. 

PHILIP  L.  WOBMELEY,  Testing  Engineer. 

EI>WIN  C.  E.  LORD,  Petrographer. 

BENJAMIN  F.  HEIDEL,  Assistant  Engineer. 

PBEVOST  HUBBAED,  Assistant  Chemist. 

WM.  W.  SNIFFIN,  Editor  and  Librarian. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1  909. 


PLATE  I. 


Issued  September  10, 1909. 

U.  S.  DEPARTMENT  OF  AGRICULTURE, 

OFFICE  OF  PUBLIC  ROADS, 

LOGAN  WALLER  PAGE,  DIRECTOR. 


EXHIBIT  OF  THE 
OFFICE  OF  PUBLIC  ROADS. 

ALASKA- YUKON -PACIFIC  EXPOSITION. 


WASHINGTON: 

GOVERNMENT     PRINTING     OFFICE 
1909. 


At 


LETTER  OE  TRANSMITTAI. 


U.  S.  DEPARTMENT  OF  AGRICULTURE, 

OFFICE  OF  PUBLIC  ROADS, 
Washington,  D.  C.,  July  lJh  1909. 

SIR:  I  have  the  honor  to  transmit  herewith  a  manuscript  con- 
taining data  explaining  the  exhibit  of  this  office  at  the  Alaska- 
Yukon-Pacific  Exposition.  The  models  of  the  various  kinds  of 
roads  are  explained  in  detail,  and  information  is  included  about 
several  different  road  machines  also.  I  believe  that  this  publication 
will  be  of  a  highly  instructive  nature,  and  it  is  therefore  requested 
that  it  be  printed  as  a  separate  bulletin  of  this  office. 
Respectfully, 

L.  W.  PAGE,  Director. 
Hon.  JAMES  WILSON, 

Secretary  of  Agriculture. 


CONTENTS. 


Page. 

Introduction 5 

Earth  roads 5 

Sand-clay  roads 7 

Gravel  roads 8 

Telford  roads 9 

Macadam  roads 10 

Completed  macadam  road 12 

Gravel  macadam  roads 12 

Macadam  roads  with  V-shaped  foundation 13 

Burnt-clay  roads 14 

Oiled  earth  roads 15 

Treated  macadam  roads .- 16 

Tarred  or  oiled  roads 16 

Tarred  roads — penetration  method ^ 16 

Tarred  roads — Glad  well  method 17 

Tar,  oil,  or  asphalt  roads 17 

Tar-slag  roads 18 

Roads  in  Rock  Creek  Park,  District  of  Columbia 18 

Road  machinery 19 

Crushing  plants 19 

Wheeled  scrapers 21 

Road  machines  or  graders 21 

Elevating  graders 23 

3 


ILLUSTRATIONS. 


PLATES. 

Page. 

PLATE  I.  Macadam  road,  Rock  Creek  Park,  District  of  Columbia Frontispiece. 

II.  Fig.  1. — Model  of  earth  road,  showing  split-log  drag  and  road  grader 

in  operation.     Fig.  2. — Model  of  sand-clay  road 8 

III.  Fig.  1  .—Model  of  gravel  road.     Fig.  2.— Model  of  Telford  road 8 

IV.  Gravel  road  in  park,  Richmond,  Ind 8 

V.  Fig.  1. — Model  of  macadam  road.     Fig.  2. — Model  of  gravel  macadam 

road 8 

VI.  Model  of  macadam  road  with  exact  model  of  road  roller  in  operation.         16 
VII.  Fig.   1. — Model    of    macadam    road    with    V-shaped    foundation. 

Fig.  2.— Model  of  burnt-clay  road :        16 

VIII.  Macadam  road  with  V-shaped  foundation  at  Russell,  Mass 16 

IX.  Fig.  1. — Model  of  oiled  earth  road.     Fig.  2. — Model  of  tarred  mac- 
adam road. 16 

X.  Fig.    1. — Model    of    tarred    macadam    road — penetration    method. 

Fig.  2. — Model  of  tarred  macadam  road — Glad  well  method 18 

XI.  Fig.  1. — Model  of  sand-bituminous  macadam  road.     Fig.  2. — Model 

of  tar-slag  macadam  road 18 

XII.  Fig.  1.— Model  of  section  of  Rock  Creek  Park,  District  of  Columbia. 

Fig.  2.— Model  of  quarry 18 

TEXT   FIGURES. 

FIG.  1 .  Exact  model  of  portable  crushing  plant  in  operation 20 

2.  Exact  model  of  wheeled  road  scraper 21 

3.  Exact  model  of  road  grader 22 

4.  Exact  model  of  elevating  road  grader 23 

4 


EXHIBIT  OF  OFFICE  OF  PUBLIC  ROADS. 

ALASKA- YUKON-PACIFIC  EXPOSITION, 


INTRODUCTION. 

In  assembling  the  very  complete  exhibit  shown  by  the  Office  of 
Public  Roads  of  the  United  States  Department  of  Agriculture,  those 
rr-ponsible  for  this  feature  of  the  Federal  Government's  contribu- 
tion to  the  Alaska- Yukon-Pacific  Exposition  have  sought  to  put  on 
view  such  striking  examples  in  miniature  of  model  roads  that  visitors 
will  not  merely  immediately  appreciate  the  beneficent  effects  of 
perfected  highways,  but  will  at  the  same  time  be  able  to  understand 
the  methods  of  their  construction. 

Visitors  will  probably  decide  that  the  most  striking  feature  of  the 
display  is  the  miniature  model  of  a  section  of  Rock  Creek  Park — 
the  most  beautiful  of  the  many  breathing  spots  in  the  District  of 
Columbia.  In  this  handsome  miniature  is  shown  not  only  some  of 
Rock  Creek  Park's  most  picturesque  landscape  features  but  also 
some  of  the  best  examples  obtainable  of  scientific  road  construction. 

The  model  includes  the  famous  Bowlder  Bridge,  the  Pebble 
Bridge,  and  one  other,  with  Rock  Creek  passing  beneath  them  and 
winding  in  and  out  among  the  hills. 

Picturesque,  and  yet  practical,  as  is  this  handsome  centerpiece  of 
the  exhibit,  it  will  not  attract  as  much  attention  from  scientific  road 
builders  as  will  the  miniature  sections  illustrating  every  type  of  road 
now  in  use. 

Among  the  types  thus  illustrated,  built  to  exact  scale,  are  macadam, 
bituminous  maoadam,  tarred  macadam,  Telford,  slag  asphalt,  slag 
tar,  oiled  macadam,  oiled  earth,  sand  clay,  burnt  clay,  and  dragged 
earth. 

Inasmuch  as  there  are  approximately  1,975,000  miles  of  earth  road 
in  the  United  States  out  of  a  total  mileage  of  2,150,000,  a  model  of 
an  earth  road  is  appropriately  first  described. 

EARTH   ROADS. 
(Platell,  fig.  1.) 

This  model  illustrates  the  construction  and  maintenance  of  an 
earth  road,  and  is  built  on  a  scale  of  1J  inches  to  the  foot,  or  one- 
eighth  full  size,  the  various  sections  which  go  to  make  up  the  com- 


OK  PUBLIC  ROADS. 

plete  model  showing  the  roadbed  and  each  succeeding  step  in  the 
construction  of  this  type  of  highway. 

It  will  be  noted  that  Section  A  shows  the  old  and  unimproved  road- 
bed. 

Section  B  illustrates  a  section  of  earth  road  under  improvement 
with  a  road  machine  or  grader,  the  width  of  the  section  shown  being 
equivalent  to  20  feet  of  finished  surface. 

Section  C  illustrates  an  earth  road  which,  though  surfaced  by  a 
road  machine,  has  rutted  under  heavy  traffic  and  is  being  maintained 
by  the  use  of  the  split-log  drag. 

In  the  road  illustrated  by  Sections  B  and  C,  the  crown,  or  slope 
from  center  to  sides,  is  equivalent  to  1  inch  to  the  foot.  The  surface  of 
the  section  labeled  "A"  is  characteristic  of  altogether  too  many  earth 
roads,  the  center  being  several  inches  lower  than  the  sides.  This 
faulty  condition  makes  it  impossible  for  the  water  to  run  from  the 
surface;  and  even  if  this  were  possible  there  are  no  roadside  ditches 
to  carry  it  away.  In  consequence,  the  road  is  usually  full  of  puddles 
and  cut  up  with  ruts  and  mud  holes. 

Section  B  illustrates  the  use  of  a  road  machine  or  grader  in  open- 
ing roadside  ditches  and  in  shaping  the  road  surface  so  it  will  shed 
water.  This  machine  is  equivalent  to  the  labor  of  many  men,  and  it 
does  the  work  far  better  than  can  be  done  with  shovels  and  picks. 

The  road  machine  should  be  used  when  the  ground  is  damp  and 
soft.  In  dry  weather  far  more  power  is  required  to  draw  it  than  in 
wet,  and  clods  when  placed  on  the  road  in  a  dry  condition  make  a 
most  unsatisfactory  surface,  turning  to  mud  with  the  first  heavy  rain. 
Because  of  these  conditions,  the  road  should  be  shaped  in  the  spring 
or  early  summer,  thus  permitting  the  roadbed  to  pack  and  bake  dur- 
ing the  heated  period  in  order  that  it  may  better  hold  up  traffic 
during  the  winter  rains. 

An  earth  road  should  have  a  width  of  at  least  20  feet — better  still, 
24  or  30.  If  the  road  be  narrow  there  is  a  tendency  to  use  but  the 
narrow  central  portion,  and  wagons  running  in  "  the  same  old  rut " 
soon  create  a  water-holding  depression.  The  surface  drainage  can  be 
provided  for  by  giving  the  road  an  average  crown  or  slope  from 
center  to  sides  of  1  inch  to  the  foot.  On  some  soils  the  crown  could 
be  even  less  than  that,  but  seldom  greater.  Unless  the  road  runs 
through  swampy  or  wet  districts,  side  ditches,  as  shown  in  Model  B, 
should  be  built.  They  can  be  made  and  maintained  with  a  road 
machine,  but  care  should  be  taken  that  they  have  a  fall  sufficient  to 
carry  the  water  along  the  side  of  the  road.  One  use  of  the  road 
machine  will  not  keep  the  ordinary  earth  road  in  permanent  repair. 
The  machine  should  be  used  several  times  during  the  spring  and  early 
summer. 


EXHIBIT  OF   OFFICE   OF   PUBLIC   ROADS.  7 

For  continuous  maintenance  the  split-log  drag  shown  in  Section  C 
has  been  devised.  This  little  model  has  been  built  to  the  same  scale 
as  the  road  model — 1J  inches  to  the  foot.  It  can  be  best  made  from 
a  log  7  or  8  inches  in  diameter  and  from  6  to  8  feet  long.  The  log 
>hould  be  carefully  split  and  the  halves  fastened  together  with  stakes, 
the  flat  sides  vertical  and  facing  to  the  front.  The  logs,  though  of 
the  same  length,  are  attached  so  that  the  end  of  the  rear  log  is  from 
16  to  20  inches  nearer  to  the"  center  of  the  road  than  the  first  one. 

An  ordinary  trace  chain  and  set  of  doubletrees  is  then  attached. 
When  the  horses  move  forward  the  drag  should  slide  along  the  road 
at  an  angle  of  about  45°,  the  forward  end  being  nearest  to  the  ditch 
and  thereby  moving  the  earth  toward  the  road  center. 

In  the  construction  of  this  implement  care  should  be  taken  to  make 
it  so  light  that  one  man  can  lift  it.  The  best  material  is  a  dry  red 
cedar  log,  though  red  elm  and  walnut  are  excellent,  and  box  elder,  soft 
maple,  or  elm  willow  are  superior  to  oak,  hickory,  or  ash.  A  board 
platform  is  usually  placed  on  the  cross  stakes,  helping  to  strengthen 
the  implement  and  giving  a  place  for  the  driver  to  stand.  After  a 
little  practice  a  man  will  learn  how  to  best  distribute  his  weight  so  as 
to  make  the  drag  cut,  spread,  and  pack  the  earth  properly. 

Dragging  up  one  side  of  the  road  and  down  the  other  across  the  ruts 
is  all  that  should  be  undertaken  the  first  time,  but  this  should  be  re- 
peated after  each  heavy  rain.  As  a  mile  of  road  can  be  dragged  in  a 
few  minutes,  the  split-log  drag  provides  a  simple  and  inexpensive 
method  of  road  maintenance.  If  it  be  used  in  conjunction  with  the 
road  machine,  fairly  good  earth  roads  can  be  secured  at  a  nominal 
expense.  If  50  cents  a  mile  for  dragging  be  considered  a  fair  figure, 
and  if  the  road  be  dragged  a  dozen  times  a  year,  it  follows  that  road 
maintenance  by  this  method  will  not  cost  more  than  $6  per  mile  per 
annum.  Some  really  remarkable  results  have  been  accomplished 
with  the  drag  without  the  aid  of  the  scraper.  Farmers'  Bulletin  321,° 
"  The  Use  of  the  Split-log  Drag  on  Earth  Roads,"  deals  fully  with 
this  subject. 

SAND-CLAY  ROADS. 

(Plate  II,  fig.  2.) 

This  model  shows  the  sand-clay  road  construction  and,  like  all 
other  models,  is  on  the  scale  of  1J  inches  to  the  foot. 

Section  A  represents  an  unimproved  sand  road  about  22  feet  wide. 

Section  B  represents  an  old  sand  road  slightly  rounded  up  to  re- 
ceive the  clay,  the  center  being  4  inches  higher  than  the  sides.  • 

0  Farmers'  bulletins  will  be  sent  free  to  any  address  in  the  United  States  on 
application  to  a  Senator  or  Representative  in  Congress  or  to  the  Secretary  of 
Agriculture,  Washington,  D.  C. 


8  EXHIBIT   OF   OFFICE   OF   PUBLIC   ROADS. 

Section  C  shows  a  portion  of  road  covered  with  clay  to  a  depth  of  6 
inches. 

Section  D  illustrates  the  harrowing  or  mixing  process. 

Section  E  shows  the  completed  road. 

An  inspection  of  this  model  shows  that  the  bottom  of  the  ditch  of 
a  completed  road  of  this  type  would  be  about  1  foot  lower  than  the 
road  at  the  center,  this  giving  an  average  slope  of  1J  inches  to  the 
foot. 

In  a  generality  of  cases  sand-clay  roads  are  built  on  sandy  founda- 
tions, and  it  is  usually  the  practice  to  place  the  clay  on  the  unim- 
proved foundation,  but  better  results  will  be  obtained  if  the  sandy 
foundation  is  given  a  slight  crown;  making  the  center  from  4  to  6 
inches  higher  than  the  side  ditches.  If  this  is  neglected,"  more  clay 
will  be  necessary  to  give  the  road  the  needed  crown  and  that  is  ex- 
pensive, especially  if  the  material  has  to  be  hauled  a  considerable 
distance. 

If  the  foundation  is  of  clay  the  process  may  be  reversed  with  sat- 
isfactory results,  the  clay  road  being  plowed  and  harrowed,  covered 
with  from  4  to  6  inches  of  sand,  and  worked  with  a  disk  or  tooth 
harrow  when  the  ground  is  wet  until  both  have  been  thoroughly 
mixed.  When  the  mixing  has  been  done  the  surface  is  brought  to 
a  crown  with  a  road  machine  and  covered  with  a  thin  layer  of  sand. 
After  the  first  two  or  three  rains  another  sand  coat  should  be  applied, 
this  method  producing  a  smooth,  cheap,  and  satisfactory  road  suit- 
able for  light  traffic. 

Farmers'  Bulletin  No.  311,  "  Sand-clay  and  Burnt-clay  Koads," 
gives  full  information  on  this  subject,  if  more  be  desired. 

GRAVEL  ROADS. 

(Plate  III,  fig.  1;  Plate  IV.) 

The  construction  of  a  gravel  road  having  shoulders  is  illustrated 
by  this  model.  The  model,  being  30  inches  wide  between  ditches,  is 
equivalent  to  a  20-foot  road,  the  traveled  way  representing  a  width 
of  12  feet. 

Section  A  represents  the  prepared  earth  roadbed,  showing  a  sub- 
grade  with  the  center  10  inches  higher  than  the  bottoms  of  the  side 
ditches  and  illustrating  at  the  same  time  the  method  of  constructing 
the  shoulders  so  as  to  hold  the  gravel  roadbed  in  position.  These 
shoulders  should  be  built  upon  the  subgrade  to  a  depth  of  about  4 
inches. 

Section  B  shows  the  first  course  of  gravel,  laid  to  a  depth  of  4 
inches  in  the  center  and  about  3  inches  at  the  sides. 

Section  C  represents  the  second  course,  the  material  being  about 
2  inches  in  depth  at  the  center  and  1J  inches  at  the  sides.  The  crown 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1909. 


PLATE 


FIG.  1.— MODEL  OF  EARTH  ROAD,  SHOWING  SPLIT-LOG  DRAG  AND  ROAD  GRADER  IN 

OPERATION. 


FIG.  2.— MODEL  OF  SAND-CLAY  ROAD. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1909. 


PLATE 


FIG.  1.— MODEL  OF  GRAVEL  ROAD. 


FIG.  2.— MODEL  OF  TELFORD  ROAD. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1909. 


PLATE  IV. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1909. 


PLATE  V. 


FIG.  1.— MODEL  OF  MACADAM  ROAD. 


FIQ.  2.— MODEL  OF  GRAVEL  MACADAM  ROAD. 


EXHIBIT   OF    OFFICE    OF    PUBLIC   ROADS.  9 

01  eeiiler  nf  the  road  thus  represented  i>  about  ()  inches  higher  than 
the  surface  of  the  road  G  feet  from  the  center,  which  gives  an  average 
-lope  of  1  inch  to  the  foot. 

There  is  financial  wisdom  in  thu>  preparing  a  foundation  for  a 
irravel  road,  because-  it  >aves  material.  If  the  gravel  is  simply  spread 
on  the  unimproved  roadbed  far  more  will  be  required,  and  if  it  is 
-pread  without  having  shoulders  constructed  to  hold  it  in  place 
wagons  will  rut  it  and  horses  kick  it  away  until  in  a  short  time  the 
ditches  will  be  full  of  gravel  and  the  denuded  road  surface  will  be 
cut  up  with  ruts. 

With  plenty  of  gravel  available,  it  is  wise  to  build  shoulders  from 
:•  to  *\  feet  in  width  and  with  a  depth  of  from  4  to  6  inches  at  the 
inside  edge,  the  depth  of  the  gravel  diminishing  toward  the  side 
ditches.  In  some  cases  thin  boards  from  4  to  6  inches  wide  are 
placed  along  the  inner  edge  of  the  shoulder  to  hold  it  in  position  until 
it  i>  packed  and  the  material  has  been  spread.  The  material  for  the 
foundation  course  is  then  spread  to  a  depth  of  from  4  to  8  inches  in 
the  center  and  from  4  to  G  inches  at  the  sides.  Creek  or  river  gravel 
may  be  used  for  this  course,  but  it  is  better  to  use  bank  or  pit  gravel, 
which  possesses  sufficient  clay  or  earthy  matter  to  bind  it  together. 

When  the  foundation  course  has  been  prepared,  the  surface  course 
>hould  fa  spread  to  a  depth  of  from  3  to  4  inches  in  the  center  and  2  to 
o  inches  at  the  sides.  It  should  be  of  the  very  best  quality  and  free 
from  large  pieces.  In  some  instances  it  is  advisable  to  screen  the 
gravel  into  two  or  three  sizes,  using  the  larger  sizes  for  the  founda- 
tion course.  All  sand,  clay,  or  earthy  matter  should  be  removed. 

The  l>est  and  cheapest  method  of  screening  gravel  is  by  the  rotary 
M-reen  having  holes  of  2^,  H.  and  f  inches.  The  best  season  for  build- 
ing gravel  roads  is  in  the  spring,  as  they  will  then  consolidate  during 
the  summer  and  be  in  better  condition  to  withstand  the  fall  and 
winter  rains. 

TELFORD   ROADS. 

•  Plate  III,  fig.  2.) 

Here  is  illustrated  the  construction  of  a  Telford  road  having  a 
width  of  12  feet,  with  shoulders  4  feet  in  width,  or  5  feet  from  the 
edge  of  the  stone  surface  to  the  bottom  of  the  side  ditches. 

Section  A  illustrates  the  prepared  subgrade,  12  feet  wide  and 
excavated  to  a  depth  of  14  inches.  The  foundation  being  5  inches 
higher  in  the  center  than  at  the  sides  gives  the  same  crown  as  the 
finished  surface. 

Section  B  represents  the  Telford  ba>e.  the  depth  of  material  being 
7  inche.-. 

Section  C  illu>trate-  the  No.  1  course  of  broken  stone,  laid  to  a 
depth  of  4  inche- 
3800—09 2 


10  EXHIBIT    OF    OFFICE    OF    PUBLIC    ROADS. 

Section  D  illustrates  the  No.  '2  or  second  course,  3  inches  deep. 

Section  E  illustrates  the  finished  road  after  being  surfaced  with 
screenings  and  stone  dust,  this  last  course  adding  nothing  to  the 
thickness  of  the  road,  as  the  fine  material  is  washed  and  rolled 
firmly  into  the  No.  2  course  of  broken  stone. 

In  the  preparation  for  a  Telford  road,  the  bed  is  excavated  from 
the  earth  surface,  as  in  the  macadam  road,  side  ditches  and  shoulder 
drains  being  built  the  same. 

The  radical  difference  between  the  Telforcl  and  the  macadam  road 
lies  in  the  paved  or  hand-laid  foundation  of  the  first  named,  the 
stones  forming  a  base  from  5  to  8  inches  thick. 

The  model  of  which  this  treats  illustrates  a  Telford  road  with  a 
base  7  inches  thick,  the  paved  foundation  being  about  two-thirds  the 
road's  total  thickness. 

Telford's  original  method  provided  for  a  flat  foundation,  his  pave- 
ments being  deeper  in  the  middle  than  at  the  sides,  the  stone  in  a 
16-foot  road  being  8  inches  deep  in  the  middle  and  5  inches  deep  at 
the  sides.  Modern  practice,  however,  calls  for  stone  of  uniform 
depth,  the  surface  of  the  base  being  parallel  to  the  surface  of  the 
finished  road. 

In  the  construction  of  such  a  base  as  that  illustrated,  the  various 
stones  should  be  of  the  following  sizes :  Length,  from  8  to  12  inches ; 
depth,  from  5  to  8  inches ;  thickness,  at  the  base  from  3  to  6  inches 
and  at  the  top  from  1  to  3  inches.  They  are  to  be  laid  lengthwise 
across  the  road  on  their  broadest  bases,  every  other  course  breaking 
joints  as  nearly  as  possible.  Uneven  points  must  be  broken  off  and 
spalls  used  to  wedge  the  surface  together  until  a  firm  foundation  has 
been  secured. 

Sections  C,  D5  and  E  are  built  in  the  same  manner  as  the  macadam 
road,  though  not  so  thick,  for  roads  possessing  a  Telford  base  do  not 
require  a  macadam  surface  of  more  than  from  4  to  6  inches  after 
consolidation. 

MACADAM   ROADS. 

(Plate  V,  tig.  1.) 

This  model  illustrates  a  macadam  road  12  feet  wide  and  surfaced 
with  8  inches  of  consolidated  stone,  the  shoulders  being  equivalent  to 
4  feet  4  inches. 

Section  A  represents  the  prepared  subgrade. 

Section  B  represents  the  first  course  of  broken  stone,  spread  to  a 
depth  of  about  5  inches. 

Section  C  represents  the  second  course,  spread  to  a  depth  of  3 
inches. 


EXHIBIT   OF   OFFICE   OF   PUBLIC   ROADS.  11 

Iii  the  model  the  crown  or  slope  of  the  foundation  is  the  same  as  in 
the  finished  road.  giving  an  average  fall  of  three-fourths  of  an  inch 
to  the  foot  from  center  to  sides. 

In  preparing  for  the  construction  of  a  road  of  this  type  it  is  ad- 
visable to  roll  the  foundation  thoroughly  when  the  soil  is  damp  so 
that  all  soft  spots  may  be  found  and  filled  and  the  ground  firmly  and 
smoothly  prepared  for  the  first  layer  of  stone.  Shoulders  are  built 
on  either  side  to  hold  the  macadam  in  place,  either  by  excavating  the 
body  of  the  old  roadbed  or  by  piling  up  the  earth  as  the  work  pro- 
gresses. The  shoulders  should  never  be  less  than  3  or  4  feet  wide,  if 
possible  6  or  8.  If  sufficiently  wide  and  having  a  slope  of  not  more 
than  1  inch  to  the  foot,  they  will  be  used  in  dry  weather  for  light 
traffic,  thus  relieving  the  macadam  of  fast  travel,  which  causes  it  to 
ravel. 

In  every  case  the  bottoms  of  the  side  ditches  should  be  lower  than 
the  road  foundation  to  insure  speedy  drainage.  If  the  road  is  built 
of  clay  or  heavy  soil  shoulder  drains  should  be  built  at  low  places 
to  lead  water  from  the  foundation.  The  drains  are  filled  with 
crushed  rock  or  gravel  and  the  side  ditches  should  be  shallow,  but 
wide,  their  construction  being  based  on  the  volume  of  water  they 
may  be  expected  to  carry. 

The  Xo.  1  crushed  rock  for  the  foundation  course  may  vary  in 
size  from  1J  to  2^  inches  in  diameter,  but  never  larger.  The  depth 
of  this  course  must  depend  upon  conditions.  If  built  on  light  grav- 
elly soil  where  light  traffic  may  be  looked  for,  a  depth  of  3  or  4  inches 
is  sufficient,  but  for  heavy  soils  and  heavy  traffic  the  course  should 
be  from  4  to  6  inches  deep  after  rolling.  For  roads  12  feet  wide 
or  less  the  depth  of  material  should  be  uniform  throughout,  but  if 
the  road  be  from  14  to  16  feet  the  total  depth  of  both  courses  may  be 
reduced  to  6  inches  for  an  8-inch  road  and  4  inches  for  a  6-inch  road. 

After  the  foundation  course  has  been  thoroughly  rolled  from  the 
sides  to  the  center,  the  second  course,  varying  in  size  from  J  to  1^ 
inches,  is  applied.  While  rock  of  inferior  quality  may  be  used  for 
the  foundation  course,  nothing  but  the  best  hard  and  tough  rock 
should  be  used  for  the  surface.  It  should  not  only  be  able  to  resist 
the  pounding  and  grinding  of  traffic,  but  should  have  a  high  cement- 
ing value  so  that  the  fine  particles  will  bind  the  surface  into  a  water - 
ahedding  cru>t. 

The  final  course  of  screenings  does  not  add  to  the  depth  of  the 
road,  which  when  completed  should  be  flush  with  the  earth  shoulders. 
The  total  depth  of  roads  of  this  type  should  vary  from  4  to  12  inches, 
construction  being  governed  by  local  conditions,  but  the  average 
depth  of  such  roads  in  the  United  States  is  not  more  than  6  inches. 


12  EXHIBIT   OF    OFFICE   OF    PUBLIC    ROADS. 

COMPLETED    MACADAM    ROAD. 
(Plate  VI.) 

By  this  model  is  illustrated  a  completed  macadam  road  with  a  12- 
foot  macadam  surface  and  shoulders  4  feet  4  inches  wide,  to  total 
road  width  of  20  feet  8  inches. 

There  is  wisdom  in  building  wide  roads,  for  they  expose  a  larger 
surface  to  traffic  and  require  less  care  than  narrow  ones,  the  traffic 
being  more  evenly  spread  because  of  the  greater  area  of  road  surface. 
The  initial  cost  of  wide  roads  is  of  course  greater  than  that  of  narrow 
ones,  but  there  is  a  saving  in  maintenance,  especially  if  the  narrow 
road  be  so  scant  that  teams  can  not  pass  and  must  travel  in  the 
same  rut. 

In  spreading  the  No.  2  or  surface-bonding  course,  the  stone  may 
vary  from  three-fourths  of  an  inch  down  to  dust.  It  is  not  necessary 
to  separate  the  dust  from  the  screenings  unless  there  be  an  excess  of 
dust.  If  too  much  is  used  the  road  will  be  sloppy  in  wet  weather  and 
dusty  in  dry,  and  if  there  is  not  a  sufficient  quantity  of  screenings  the 
road  will  quickly  ravel,  especially  under  fast  automobile  traffic. 

Care  and  judgment  must  be  exercised  in  determining  the  proper 
amount  of  screenings  and  also  in  spreading  them.  One  thin  layer 
should  be  spread  and  rolled,  and  after  it  has  been  thoroughly 
sprinkled  and  rolled  another  should  be  spread.  By  continuing  this 
process  until  all  voids  are  filled  and  the  surface  has  been  thoroughly 
consolidated  a  waterproof  surface  will  be  secured. 

On  this  model  is  shown  a  miniature  steam  roller,  the  presence  of 
this  tiny  facsimile  of  its  gigantic  prototype  emphasizing  the  impor- 
tance of  road  rolling.  In  the  long  run  better  aiid  cheaper  work  can 
be  done  v,  ith  a  steam  than  with  a  horse  roller,  and  one  may  also  be 
used  to  advantage  in  road  repair  w^ork. 

If  the  road  surface  becomes  uneven  or  rutted  it  can  be  spiked  by 
teeth  placed  in  the  wheels  of  the  roller.  Then  the  surface  can  be 
leveled  off  and  resurfaced  with  another  course  of  No.  2  stone,  after 
which  it  may  be  rolled  and  again  treated  with  screenings. 

Farmers'  Bulletin  No.  338,  "  Macadam  Roads,''  gives  much  addi- 
tional information  on  this  subject. 

GRAVEL    MACADAM    ROADS. 
(Plate  V.  fig.  2.) 

This  model  illustrates  the  construction  of  a  gravel  macadam  road, 
built  in  layers  after  the  macadam  method,  the  miniature  represent- 
ing a  12-foot  road  with  4-foot  shoulders  on  either  side,  the  shoulder 
depth  being  4  inches. 


KX  II I  HIT   OF    OFFICE    OF    PUBLIC    ROADS.  13 

Section  .V  >hm\>  the  prepared  subgrade,  the  excavation  represent- 
ing a  width  of  \'2  feet  and  a  depth  of  8  inches. 

Section  IS  represents  the  first  course  of  gravel,  spread  to  a  depth 
nf  :>  inches. 

Section  C  shows  the  >econd  course  of  h'ner  gravel,  equivalent  to  a 
depth  of  3  inches  in  the  completed  road,  the  shoulders  represented 
being  equivalent  to  a  width  of  4i  feet.  The  crown  or  slope  of  the 
foundation  is  5  inches  higher  in  the  center  than  at  the  sides,  an  aver- 
age of  three- fourths  of  an  inch  to  the  foot. 

In  constructing  this  type  the  foundation  should  be  thoroughly 
rolled  before  any  gravel  i-  spread,  in  order  that  all  depressions  may 
be  found  and  filled. 

Side  ditches  should  be  lower  than  the  lowest  part  of  the  road 
foundation,  and  drains  should  be  cut  through  the  shoulder  and  filled 
with  gravel  if  the  road  be  built  of  clay  or  other  heavy  soil.  They 
should  be  placed  200  or  300  feet  apart,  or  at  all  low  places,  their  loca- 
tions being  governed  by  conditions.  Creek  or  river  gravel  from 
which  clay  or  soil  has  been  removed  may  be  used  for  the  foundation 
course,  provided  gravel  possessing  sufficient  binding  clay  is  used  for 
the  surface  course. 

In  frequent  instances  good  results  are  secured  by  separating  the 
gravel  into  three  sizes,  as  for  a  macadam  road,  using  the  larger  sizes 
for  the  foundation  and  the  finer  for  the  second  and  the  binder  course^ 
The  gravel  should  be  wet  when  spread  and  rolled.  The  surface  course 
should  be  composed  of  material  not  larger  than  from  1  to  H  inches 
in  diameter,  and  enough  clay  or  fine  gravel  should  be  added  to  it  to 
bind  it  together.  If  too  much  clay  be  present,  however,  the  road  will 
be  muddy  and  sticky  in  wet  weather  and  dusty  in  dry. 

A  judicious  use  of  the  split-log  drag  will  keep  this  type  of  road 
in  repair  at  a  small  cost. 

.MACADAM    ROADS    WITH    VSIIAI'KD    FOTNDATIOX. 

•  Plate  VII.  fig.   1  :   Plate   VIII. » 

Here  is  illustrated  a  12- foot  macadam  road  with  a  V-shaped  foun- 
dation which  is  constructed  of  field  stones  or  bowlders. 

Section  A  shows  the  prepared  subgrade  ready  to  receive  the  foun- 
dation stone.  The  depth  of  shoulders  is  1  foot  and  the  center  of 
the  foundation  is  10  inches  below  the  bottom  of  these  shoulders. 
tin*  slope  toward  the  center  being  equivalent  to  1^  inches  to  the  foot. 

Section  B  represents  the  completed  foundation. 

Section  ('  represents  the  first  course  of  macadam. 

Section  I)  represents  the  regular  Xo.  '2  course  of  macadam  laid 
to  a  depth  of  3  inches. 


14  EXHIBIT   OF    OFFICE   OF    PUBLIC    ROADS. 

Section  E  shows  the  completed  surface  of  a  macadam  road  bonded 
with  screenings  and  dust. 

The  V-shaped  macadam  road  has  been  constructed  by  the  Massa- 
chusetts Highway  Commission  as  a  substitute  for  the  Telford 
method.  It  is  especially  good  in  heavy  clay  soils  or  in  low  swampy 
places  where  .the  foundation  can  not  be  depended  upon  to  hold  up 
the  regular  macadam  road. 

In  this  type  of  road  the  foundation  is  sloped  from  the  sides  to  the 
center  rather  than  from  center  to  sides,  as  in  all  other  methods  of  road 
construction,  and  shoulder  drains  are  cut  at  low  places  and  filled  with 
bowlders  or  gravel.  Through  these  drains  the  water  which  makes  its 
way  to  the  foundation  is  conveyed  to  the  side  ditches. 

Field  stones,  bowlders,  or  broken  stone  secured  from  excavations  in 
the  road  are  used  in  building  the  foundation,  the  larger  pieces  being 
placed  in  the  bottom  and  the  smaller  ones  on  the  surface.  The  total 
depth  of  the  foundation  is  from  18  inches  to  2  feet  in  the  center  and 
from  4  to  8  inches  at  the  sides.  The  foundation  is  given  a  slope  or 
crown  and  the  crushed  stone  is  then  placed  on  the  road,  as  illustrated 
by  Plate  Y,  figure  1,  and  Plate  VI. 

In  the  completed  road  the  crown  appears  to  be  higher  than  in  the 
ordinary  macadam  road,  but  this  is  on  account  of  the  deep  side 
ditches,  the  crown  really  being  only  about  5  inches  higher  at  the 
center  than  at  the  sides — an  average  of  about  three-fourths  of  an  inch 
to  the  foot. 

In  the  model  the  depth  of  the  first  and  second  courses  is  equivalent 
to  8  inches,  but  in  actual  construction  the  depth  of  these  two  courses 
frequently  amounts  to  no  more  than  4  to  6  inches. 

BURNT-CLAY   ROADS. 
(Plate  VII,  fig.  2.) 

This  model  illustrates  the  building  of  a  burnt-clay  road,  the  model 
being  the  equivalent  of  a  road  20  feet  between  ditches,  with  a  burnt - 
clay  surface  16  feet  wide. 

Section  A  shows  the  old  roadbed  plowed  up  and  after  ridges  18 
inches  high  and  4  feet  apart  have  been  thrown  across  the  road. 

Section  B  shows  the  method  of  stacking  the  clay  and  wood  pre- 
paratory to  burning.  A  layer  of  4-foot  cord  wood  is  placed  across 
the  ridges  and  lengthwise  of  the  road.  Then  a  second  layer  is  laid 
across  the  road,  and  on  this  a  few  clods  of  clay  are  placed.  A  third 
layer  of  wood  is  then  placed  with  the  sticks  running  lengthwise 
along  the  highway,  and  18  inches  of  clay  from  the  roadside  ditches 
is  placed  upon  it.  Then  the  flues  between  the  ridges  are  filled  with 
bark  and  light  wood  and  fire  is  applied.  It  will  require  from  twenty- 
four  to  thirty-six  hours  to  complete  the  burning  of  one  section. 


KXHIBIT   OF   OFFICE   OF   PUBLIC   ROADS.  15 

Section  C  shows  a  piece  of  road  after  it  has  been  burned  and 
before  being  spread  and  roiled.  It  will  be  noted  that  the  burning 
removes  the  stickiness  or  plasticity  of  the  clay  and  leaves  it  in  hard 
clinker-like  lumps. 

Section  D  illustrates  the  finished  road,  smooth  and  firm  and  well 
crowned,  the  slope  being  1  inch  to  the  foot. 

The  burnt-clay  road,  which  is  confined  to  the  Mississippi  Delta 
States  where  stone  and  gravel  is  scarce  and  "  gumbo  "  or  "  buckshot  " 
<  Inv  plentiful,  is  never  muddy  in  winter  unless  mud  be  carried  to  it 
from  other  roads. 

Farmers'  Bulletin  No.  311,  "  Sand-clay  and  Burnt-clay  Roads," 
gives  full  information  about  this  type  of  highway,  if  more  be 
desired. 

OILED   EARTH   ROADS. 

<  Plate  IX.  fi£.  1.) 

This  model  shows  the  construction  of  an  oiled  earth  road,  the  type 
now  popular  in  the  California  orange  belt. 

Section  A  shows  the  dusty  road  before  improvement. 

Section  B  shows  the  road  plowed  to  a  depth  of  6  inches. 

Section  C  illustrates  the  application  of  oil  to  the  plowed  road. 

Section  D  shows  the  road  after  being  harrowed  and  the  oil  worked 
into  the  loose  soil. 

Section  E  shows  the  completed  road  after  having  been  thorough!}- 
rolled,  the  crown  representing  a  slope  of  three-fourths  inch  to  the 
foot. 

In  preparing  this  road  for  its  final  treatment  it  is  necessary  first  to 
bring  the  surface  to  the  same  general  crown  as  for  an  ordinary  earth 
road  and  then  to  plow  and  harrow  it  until  all  clods,  are  broken  up. 
After  that  has  been  done  the  hot  oil  is  applied  from  a  tank  wagon  at 
the  proportion  of  1  gallon  to  the  square  yard,  the  oil  being  thor- 
oughly mixed  with  the  earth  by  means  of  a  harrow  and  a  road  grader. 
To  facilitate  proper  mixing  it  is  frequently  advantageous  to  apply  a 
considerable  quantity  of  water. 

After  this  first  mixing  the  road  is  again  plowed  and  a  second  and 
then  a  third  application  of  oil  is  made.  If,  when  the  finished  road  is 
being  rolled  and  compacted,  any  excess  oil  shows  on  the  surface,  it 
should  be  taken  up  with  fresh  earth.  In  compacting  the  oiled  earth 
road  it  is  wise  to  use  a  tamping  roller,  which  consists  of  a  drum  car- 
rying a  large  number  of  blunt-headed  spikes  in  its  circumference. 
This  device  compacts  the  road  from  the  bottom  up  rather  than  from 
the  top  down,  as  is  done  by  an  ordinarv  roller. 


16  EXHIBIT   OF    OFFICE    OF    PUBLIC    ROADS. 

TREATED  MACADAM   ROADS. 
TARRED    OR    OILED    ROADS. 
(Plate  IX.  fix.  2.) 

The  surface  treatment  of  an  old  macadam  road  with  tar  or  oil  is 
shown  by  this  model. 

Section  A  shows  the  macadam  surface  before  treatment. 

Section  B  shows  the  surface  swept  free  from  dust  and  detritus. 

Section  C  shows  the  application  of  hot  tar  to  the  swept  surface  at 
a  ratio  of  from  three-tenths  to  seven-tenths  gallon  per  square  yard. 

Section  D  shows  the  final  application  of  sand  to  the  tarred  surface, 
thus  completing  the  treatment. 

In  applying  the  tar  or  oil  a  number  of  methods  may  be  adopted- 
pouring  by  hand  or  through  the  use  of  a  sprinkling  wagon.  The 
liquid  should  be  thoroughly  broomed  into  the  old  surface  before  the 
sand  is  applied  to  insure  perfect  cohesion.  Before  any  application 
of  oil  or  tar  be  made  all  loose  material  should  be  removed  and  the 
road  surface  be  absolutely  dry.  Enough  sand  should  be  applied  to 
take  up  what  excess  of  tar  may  be  left  on  the  surface. 

TARRED    ROADS PENETRATION    METHOD. 

(Plate  X,  fig.  1.) 

The  construction  of  a  tar  macadam  road  built  according  to  the 
penetration  method  is  here  shown — the  model  being  equivalent  to 
a  macadam  surface  12  feet  wide. 

Section  A  represents  the  prepared  subgrade,  excavated  to  a  width 
of  12  feet  and  a  depth  of  6  inches. 

Section  B  represents  the  first  course  of  No.  1  stone,  placed  to  a  depth 
of  4  inches. 

Section  C  represents  the  second  course  of  No.  2  stone,  spread  to  a 
depth  of  2  inches. 

Section  D  shows  the  application  of  tar  to  the  No.  2  course. 

Section  E  shows  the  application  of  screenings,  which  completes 
the  road  surface,  the  crown  of  the  finished  road  representing  an 
average  fall  of  one-half  inch  to  the  foot. 

The  construction  of  this  road,  to  a  certain  point,  is  the  same  as 
an  ordinary  macadam  road — Nos.  1  and  2  courses  being  so  built. 
Before  the  screenings  are  applied,  however,  hot  tar  is  flushed  into 
the  No.  2  course  at  the  ratio  of  from  1  to  1^  gallons  to  the  square  yard. 
When  the  screenings  have  been  spread  the  road  is  rolled  until  thor- 
oughly compacted  and  it  is  then  ready  for  traffic. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1909. 


PLATE  VI. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1909. 


PLATE  VII. 


FIG.  1.— MODEL  OF  MACADAM  ROAD  WITH  V-SHAPED  FOUNDATION. 


FIG.  2.— MODEL  OF  BURNT-CLAY  ROAD. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1909. 


PLATE  VIII. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1909. 


PLATE  IX. 


FIG.  1.— MODEL  OF  OILED  EARTH  ROAD. 


FIG.  2.— MODEL  OF  TARRED  MACADAM  ROAD. 


EXHIBIT   OF   OFFICE   OF   PUBLIC   ROADS.  17 

TARRED   ROADS GLADWELL   METHOD. 

(Plate  X,  fig.  2.) 

This  model  illustrates  a  tarred  macadam  road  built  according  to 
the  Gladwell  method  and,  like  the  other  models,  is  on  a  scale  of  1J 
inches  to  the  foot,  the  macadam  surface  being  equivalent  to  a  width 
of  12  feet. 

Section  A  shows  a  No.  1  course  of  stone  which  has  been  placed  on 
the  subgrade  as  in  the  ordinary  macadam  construction. 

Section  B  represents  the  application  of  1  inch  of  tarred  screenings. 

Section  C  represents  the  application  of  2  inches  of  No.  2  stones. 

Section  D  shows  that  layer  painted  with  hot  tar. 

Section  E  shows  the  application  of  a  final  coat  of  screenings.  These 
being  rolled  down  add  nothing  to  the  thickness  of  the  road,  which, 
when  thus  completed,  is  crowned  with  a  slope  of  one-half  inch  to 
the  foot. 

The  peculiar  departure  that  makes  this  road  distinctive  begins 
after  the  first  course  of  No.  1  stone — the  foundation  course — has  been 
laid.  On  that  the  course  of  tarred  screenings  is  spread  and  then  the 
layer  of  No.  2  stone,  and  when  rolled  the  screenings  are  forced  down- 
ward into  the  foundation  course  and  upward  into  the  surface  course, 
thus  binding  both  together.  Rolling  should  be  continued  until  the 
tarred  screenings  appear  on  the  surface,  and  then  a  light  sprinkling 
of  screenings  or  tarred  sand  may  be  applied  to  fill  the  surface  voids. 

The  final  operation  is  the  painting  of  the  No.  2  course  with  hot 
tar  at  the  ratio  of  from  one-half  to  seven-tenths  gallon  a  square  yard 
and  the  application  of  dry  screenings  to  take  up  all  excess  of  tar 
and  to  give  a  proper  finish. 

TAR,  OIL,  OR  ASPHALT  ROADS. 

(Plate  XI,  fig.  1.) 

This  model  illustrates  the  construction  of  a  tar,  oil,  or  asphalt  mac- 
adam road,  having  a  macadam  surface  12  feet  wide. 

Section  A  illustrates  the  prepared  subgrade  excavated  to  a  depth  of 
6  inches  and  a  width  of  12  feet. 

Section  B  represents  the  first  course  of  No.  1  stone,  placed  to  a 
depth  of  4  inches. 

Section  C  represents  the  second  course  of  bitumen-covered  stone, 
spread  to  a  depth  of  about  2  inches. 

Section  D  represents  the  application  of  about  a  one-fourth-inch 
layer  of  bitumen-covered  sand,  which  being  rolled  firmly  into  the  sur- 
face voids  adds  nothing  to  the  thickness  of  the  road. 

Section  E  shows  the  application  of  an  extremely  light  coat  of  stone 
dust,  which  is  the  finished  application  and  which  should  leave  the 
road  with  a  sloping  crown  of  one-half  inch  to  the  foot. 


18  EXHIBIT   OF   OFFICE   OF   PUBLIC   EOADS. 

The  subgrade  is  as  in  other  macadam  roads,  the  course  of  bitumen- 
covered  stones  being  prepared  by  applying  sufficient  hot  bitumen  to 
cover  a  graded  mineral  aggregate  when  mixed.  This  graded  aggre- 
gate is  composed  of  No.  2  stone  and  stone  ranging  in  size  from  three- 
fourths  of  an  inch  to  dust  in  proportions  of  960  pounds  to  350  pounds. 

Before  applying  the  bitumen-covered  sand,  this  course  must  be 
thoroughly  rolled  and  the  sand  then  applied  in  such  quantities  that 
it  will  fill  the  surface  voids  and  bring  the  surface  to  a  smooth  and  even 
condition. 

The  final  coat  of  stone  dust  is  merely  applied  for  the  purpose  of 
taking  up  any  excess  of  bitumen  and  of  giving  the  road  a  pleasing 
appearance. 

TAR-SLAG  ROADS. 
(Plate  XI,  fig.  2.) 

This  model  shows  the  construction  of  a  tar-slag  macadam  road,  the 
slag  surface  being  equivalent  to  a  width  of  12  feet. 

Section  A  represents  the  subgrade,  prepared  as  for  the  ordinary 
macadam  road,  being  excavated  to  a  width  of  12  feet  and  a  depth  of 
6  inches. 

Section  B  represents  the  first  course  of  broken  slag,  placed  to  a 
depth  of  4  inches. 

Section  C  represents  the  second  course  of  broken  slag,  the  slag 
being  the  regular  No.  2  size,  coated  with  tar  before  spreading,  and 
placed  to  a  depth  of  2  inches. 

Section  D  represents  the  No.  2  slag,  which  has  been  rolled  and 
painted  with  tar. 

Section  E  shows  the  application  of  a  light  covering  of  slag  screen- 
ings which,  being  rolled  into  the  surface  voids  of  Section  D,  adds 
nothing  to  the  road  thickness,  the  road  crown  when  finished  repre- 
senting an  average  slope  of  about  one-half  inch  to  the  foot. 

The  method  employed  in  making  this  road  is  similar  to  that  in  an 
ordinary  macadam  road  except  that  no  water  is  used  and  the  second 
course  is  covered  with  hot  tar  before  being  applied,  the  slag  and  tar 
being  mixed  either  by  machinery  or  by  hand.  The  amount  of  tar 
will  vary  with  the  quantity  of  slag,  though  usually  averaging  about 
5  per  cent  of  the  weight  of  the  slag. 

When  the  course  represented  by  Section  D  has  been  rolled,  it  is 
painted  with  a  light  coat  of  tar  to  insure  a  perfect  adhesion  of  the 
coat  of  screenings,  which  is  last  applied  and  thoroughly  rolled. 

ROADS  IN  BOCK  CREEK  PARK,   DISTRICT  OF   COLUMBIA. 
(Plate  I;  Plate  XII,  fig.  1.) 

This  is  a  model  in  miniature  of  a  portion  of  the  handsome  Kock 
Creek  P5rk  at  the  National  Capital,  and  it  shows  the  relationship  of 
roads  and  bridges  to  rugged  topography. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr ,  1909. 


PLATE  X. 


FIG.  1.— MODEL  OF  TARRED  MACADAM  ROAD— PENETRATION  METHOD. 


FIQ.  2.— MODEL  OF  TARRED  MACADAM  ROAD— GLADWELL  METHOD. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1909. 


PLATE  XI. 


FIG.  1.— MODEL  OF  SAND-BITUMINOUS  MACADAM  ROAD. 


FIG.  2.— MODEL  OF  TAR-SLAG  MACADAM  ROAD. 


Exhibit  Office  of  Public  Roads,  U.  S.  Dept.  of  Agr.,  1909. 


PLATE  XII. 


FIG.  1.— MODEL  OF  SECTION  OF  ROCK  CREEK  PARK,  DISTRICT  OF  COLUMBIA. 


FIG.  2.— MODEL  OF  QUARRY. 


EXHIBIT   OF   OFFICE   OF   PUBLIC   ROADS.  19 

The  model  is  on  the  scale  of  1  inch  to  20  feet,  and  it  represents  a 
rectangle  about  1,000  feet  wkle  and  2,500  feet  long.  The  highways 
which  cut  the  park  are  splendid  examples  of  the  road-builder's  art, 
the  grades  being  eas^  and  the  roadbeds  being  surfaced  with  trap  rock 
of  the  best  quality.  Bowlder  Bridge  and  Pebble  Bridge,  which  are 
shown  in  the  model,  are  picturesque  ornaments,  Bowlder  Bridge, 
which  fits  harmoniously  into  the  scene,  being  especially  attractive  in 
coloring,  as  it  was  constructed  from  bowlders  picked  from  the  bed 
of  the  stream. 

Of  all  its  attractive  features,  visitors  to  Rock  Creek  Park  will  find 
none  more  pleasing  than  the  section  of  road  which  runs  past  Pierce's 
old  vine-covered  mill  with  its  broken  wheel  and  shimmering  mill 
pond.  For  7  miles  this  road  follows  the  tortuous  windings  of  Rock 
Creek,  each  twist  and  turn  revealing  a  new  vista  of  wild  and  pictur- 
esque beauty. 

Passing  from  the  gorge  through  which  the  stream  flows,  this  road 
branches  into  others,  which  by  slight  detours  and  gentle  inclines  lead 
to  high  plateaus  from  which  the  stately  Capitol  may  be  seen  in  the 
distance. 

KOAD  MACHINERY. 
CRUSHING  PLANTS. 

This  model  (fig.  1)  represents  a  portable  stone-crushing  plant,  an 
indispensable  adjunct  to  the  building  of  first-class  stone  roads,  for 
if  such  work  is  to  be  well  and  cheaply  done,  it  follows  that  the  plant 
must  be  complete  and  conveniently  arranged. 

When  possible  the  crusher  should  be  so  near  the  quarry  that  the 
rock  may  be  sent  down  grade  in  tram  cars  and  delivered  to  the 
crusher's  mouth  by  gravity,  thus  rendering  lifting  it  by  hand  un- 
necessary. The  crusher  should  be  provided  with  an  elevator  and  with 
screens  for  separating  the  material  into  proper  sizes.  The  screens 
should  be  divided  so  that  through  the  section  near  the  upper  end 
fragments  not  exceeding  one-half  inch  will  pass,  the  second  section 
allowing  the  passage  of  stones  of  1J  inches,  and  the  third  section 
permitting  stones  2^  inches  to  make  their  way.  Any  larger  stones  will 
be  forced  through  the  open  end  of  the  screen,  from  which  they  will 
drop  into  the  tailings  conveyor,  being  finally  crushed  or  eliminated 
from  the  work.  The  jaws  of  the  crusher  should  be  set  so  as  to  make 
as  few  tailings  as  possible,  and  the  lengths  of  the  screen  sections 
should  be  adjusted  to  the  same  purpose. 

When  soft  stones  are  being  crushed  a  dust  jacket,  having  one-half 
inch  mesh,  may  be  placed  over  the  first  section  to  eliminate  dust  from 
the  screenings. 


20 


EXHIBIT   OF    OFFICE   OF   PUBLIC    KOADS. 


For  receiving  the  various  sizes  of  crushed  rock,  bins  with  slanting 
metal  bottoms  and  sliding  doors  should  be  provided,  so  that  the  ma- 
terial can  be  loaded  into  wagons  by  gravity. 

Two  types  of  crusher  are  now  commonly  used,  one  the  jaw  crusher, 
as  shown  in  figure  1,  and  the  gyratory  crusher.  The  jaw  crusher  is 
generally  used  for  portable  plants. 

In  this  machine  one  of  the  jawrs  moves  backward  and  forward  by 
means  of  a  toggle  joint  and  an  eccentric,  the  stone  descending  as  the 
jaw  recedes.  As  it  returns,  it  catches  the  stone  and  crushes  it.  The 


FIG.  1. — Exact  model  of  portable  crushing  plant  in  operation. 

maximum  size  of  the  product  is  determined  by  the  distance  the  jaw 
plates  are  apart  at  the  lower  edge. 

The  gyratory  crusher  consists  of  a  solid  conical  iron  shaft,  sup- 
ported with  a  heavy  mass  somewhat  like  an  inverted  bell.  By  means 
of  an  eccentric  a  rotary  motion  is  given  the  shaft  so  that  every  point 
of  its  surface  is  successively  brought  near  the  surface  of  the  "  bell," 
the  rock  caught  between  shaft  and  bell  being  crushed. 

The  gyratory  crusher  will  not  produce  as  many  flat  pieces  or  tail- 
ings as  the  jaw  crusher,  because  the  stones  have  to  come  in  contact 
with  two  curved  surfaces  at  the  same  time  before  they  are  broken. 


EXHIBIT   OF   OFFICE   OF   PUBLIC   ROADS.  21 

WHEELED  SCRAPERS. 

This  model  (fig.  2)  illustrates  a  wheeled  scraper,  which  consists  of 
a  steel  box  mounted  on  wheels,  provided  with  levers  for  raising, 
lowering,  and  dumping,  all  of  these  movements  being  made  without 
stopping  the  team. 

Wheeled  scrapers  are  made  in  three  sizes,  having  capacities  of  9, 12, 
and  16  cubic  feet,  respectively.  They  are  used  in  building  earth 
roads,  or  in  preparing  the  subgrade  for  macadam  roads,  especially 


FIG.  2. — Exact  model  of  wheeled  road  scraper. 

where  cuts  and  fills  are  to  be  made  and  where  the  material  can  not  be 
conveniently  handled  with  drag  scrapers. 

ROAD    MACHINES  OR   GRADERS. 

This  model  (fig.  3)  shows  in  miniature  a  machine  which  is  exten- 
sively used  in  building  and  in  preparing  the  subgrade  for  macadam 
roads.  As  will  be  noted,  it  consists  of  a  frame  carried  on  wheels 
which  support  an  adjustable  scraper  blade,  the  front  end  of  which 
plows  a  furrow,  while  the  rear  end  pushes  the  earth  toward  the  center 
or  distributes  it  smoothly.  The  blade  may  be  set  at  any  angle  or 
tilted  either  backward  or  forward. 

In  building  the  earth  road  with  the  road  machine  a  furrow  is  first 
plowed  with  the  point  of  the  blade  \vhere  the  outside  of  the  ditch 


22 


EXHIBIT    OF    OFFICE   OF   PUBLIC   ROADS. 


is  to  be  located.  The  blade  may  be  made  to  penetrate  hard  or  stony 
ground  by  elevating  the  rear  end  considerably  and  by  using  only 
the  point  of  the  blade  for  such  plowing. 

On  the  second  round,  with  the  front  and  rear  wheels  in  line,  the 
team  should  be  driven  so  that  the  point  of  the  blade  will  follow  the 
furrow  made  by  the  first  round,  plowing  a  full  furrow  with  the 
advance  end  of  the  blade  and  dropping  the  rear  end  somewhat  lower 
than  before. 

When  the  third  round  is  made  the  machine  should  be  guided 
toward  the  middle  of  the  road,  thus  shoving  the  earth  previously 
plowed  toward  the  center.  This  is  done  by  slightly  elevating  the 
rear  end  of  the  blade  to  allow  the  earth  to  distribute  under  it  and 
to  give  the  necessary  crown  to  the  sides  of  the  road.  Three  times 


FIG.  3. — Exact  model  of  road  grader. 

this  operation  should  be  repeated  until  three  layers  of  earth  have 
been  moved  to  the  road  center,  but  care  should  be  taken  not  to  leave 
a  ridge  in  the  center. 

It  is  advisable  to  use  the  machine  when  the  ground  is  soft,  the 
grading  being  done  in  the  early  summer  when  possible  in  order  to 
give  the  loose  earth  time  to  settle  and  pack  before  the  fall  rains.  If 
the  work  be  done  in  the  fall  no  more  than  3  or  4  inches  of  loose 
earth  should  be  put  on  at  one  working. 

If  the  side  of  the  road  is  covered  with  sod,  this  should  be  cut  as 
thin  as  possible  with  the  road  machine  and  moved  toward  the  center 
of  the  road,  and  the  earth  from  the  side  ditches  will  then  cover  it 
to  such  a  depth  that  it  can  not  be  objectionable. 

From  4  to  6  inches  of  loose  earth  is  sufficient  for  one  working. 


EXHIBIT   OF   OFFICE   OF   PUBLIC   ROADS.  23 


ELEVATING    GRADERS. 


Figure  4  shows  a  miniature  of  the  elevating  grader,  which  con- 
sists of  a  frame  carried  upon  four  wheels,  the  grading  machinery 
consisting  of  a  plow  and  a  wide  traveling  belt,  this  latter  being  in 
sections  and  so  adjusted  that  it  may  be  raised  or  lowered. 

The  type  of  grader  used  in  ordinary  highway  work  will  deliver 
earth  T  feet  vertically  and  from  14  to  17  feet  horizontally,  the  plow 
loosening  the  soil  and  passing  it  directly  to  the  belt,  which  delivers 
it  either  to  an  embankment  or  to  wagons. 

By  changing  the  length  of  the  belt  and  properly  distributing  the 
earth  the  machine  will  build  either  a  broad  low  embankment  from 
a  deep  narrow  cutting  or  a  narrow  high  embankment  from  a  broad 
shallow  cutting. 


FIG.  4. — Exact  model  of  elevating  road  grader. 

This  machine  is  especially  adapted  to  building  earth  roads  in 
prairie  country  or  on  flat  lands  where  it  is  desirable  to  raise  the  road 
above  the  surrounding  ground  or  the  water  table. 

Like  nearly  all  other  machinery,  the  elevating  grader  comes  in 
various  sizes,  the  largest  usually  being  propelled  by  12  horses,  8 
pulling  and  4  pushing.  The  smaller  one,  which  is  generally  used, 
is  operated  by  8  horses.  A  traction  engine  may  be  used  instead  of 
horses,  and  it  will  be  found  to  be  cheaper. 

In  building  roads  or  embankments  this  machine  has  a  capacity  of 
about  1.000  cubic  yards  each  ten  hours  and  about  600  yards  when 
loading  into  wagons.  It  will  grade  about  a  quarter  of  a  mile  of 
ordinary  prairie  road  per  day  to  a  width  of  25  to  30  feet  with  a  depth 
of  1  foot  in  the  center. 

o 


(iaylord  Mro-;. 

Makers 

Syracuse,**.  V. 

"  PAT.  JAN.  21.  1908 


T'E 


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